Vibratory strand reference apparatus with longitudinal component drive



Apnl 5, 1949. T. M. FERRILL, JR 2,456,018 VIBRATOHY STRAND REFERENCE APPARATUS WITH LONGITUDINL COMPONENT DRIVE Filed Aug. 2, 194s 27 Z5 #7 SII/FTER 5 l iNvENroR Tvc/9ms M. F ERR/L (/Q.

Patented Apr. 5, 1949 UNITED STATES PATENT OFFICE VIBRATORY ST RAND REFERENCE APPARA- TUS WITH LONGITUDINAL COMPONENT DRIVE Thomas M.

Ferrill, Jr., Hempstead, N. Y., assignor Sperry Corporation, re

a corporation of Application August 2, 1946, Serial No. 688,157

21 Claims.

ment of a vibrating As set forth in patent application Serial No. 556,186, led September 28, 1944, by the present inventor, there has heretofore been provided a stable reference system fine-gauge strand of elastic material stretched 1 pacitor pick-olf elements energized by a direct voltage source were provided in that apparatus e evacuated supporting structure and the trand erence purposes.

ln'object of the present invention is to provide roved vibratory stable reference apparatus, l more particularly, it is an object of this `intion to provide vibratory stable reference apitus wherein the long-time stability of the plane 55 (Cl. 318i-489) 2 of vibration of a vibratory element is not directly limited by the Q thereof, but may be carried appreciably beyond the limits normally imposed by the energy losses per cycle of vibration of the vibratory element.

e. g., with a Q of the order of 50,000 to 100,000. In accordance with a further feature of this invention, the longitudinal drive component may be supplied by magnetostrictive action which involves ma-gnetostrictlve effects coil arranged to i elds substantially along the axis As has been set plication Serial thereof.

'I'he invention in another of its aspects relates to novel features of the instrumentalities described herein for achieving the principal objects of the invention and to novel principles employed in those instrumentalities, whether or not these features and principles are used for the said principal objects or in the said field.

A vfurther object of the invention is to provide improved apparatus and instrumentalities embodying novel features and principles, adapted for use in realizing the above objects and also adapted for use in other fields.

Further objects will become apparent and the above objects and features will be more fully understood by reference. to the following description of an embodiment of the present invention, taken in conjunction with the drawing, wherein Fig. 1 is a schematic representation of vibratory stable reference apparatus constructed in accordance with the present invention, is a fragmentary view representing a modification of the structure shown in Fig. 1.

Fig. 1 illustrates vibratory stable reference apparatus including a rigid envelope I I of dielectric material such as glass or quartz, within which is suspended a slender strand I3 of elastic material such as nickel or a nickel-iron alloy, or an alloy which may contain nickel, iron and cobalt or chromium, if desired. Such a material is susceptible to magnetostrictive elongation and contraction, and is selected primarily for this property. The strand I3 may be attached at its ends to ferrules I5 and I1 sealed to the ends of the envelope II.

An arrangement is provided for maintaining the strand I3 in transverse planar vibration.- This arrangement includes a capacitor pick-off element I9 energized by a source 2l through a resistor 23, and coupled through a capacitor 25 to the input circuit of an amplier 21. Amplifier 21 has its output circuit coupled through a transformer 29 both to the strand I3 and to a magnetostrictive driving system including coils 3i and 33. The transformer 29 includes one secondary winding 35 connected to a potentiometer 31, the movable tap 39 of the potentiometer and a. grounded terminal 4I thereof being connected respectively to the upper ferrule I5 and the grounded lower ferrule I1, for application of alternating driving voltage directly to strand I3 and hence, for passage of alternating current therethrough. This alternating current through the strand I3 reacts with the component of an ambient magnetic field perpendicular to the strand I3 for inducing the strand I3 to vibrate in a plane through strand I3 perpendicular to the ambient magnetic field component.

A further secondary winding 43 of the transformer 29 is connected to the input circuit of a phase shifter 45, and the output circuit of the phase shifter is connected through a potentiometer 41 to the magnetostrictive driving coils 3| and 33. Coils 3I, 33 are arranged in the envelope II in substantially coaxial positional arrangement with the strand I3, so that they produce magnetic fields extending along the strand. Through the phase shifter 45 and the potentiometer 41, these coils are energized with alternating current at the frequency of the current through'the strand I3; and accordingly, they produce alternating magnetic fields along the strand I3 of this frequency. The magnetostrictive drive is nonpolarized, however, so that the strand I3 responds in the same way to a positive half-cycle of the alternating current through the coils 3|, 33 as it does to the negative half-cycle of the current. Accordingly, two cycles of contractive and expansive forces are produced in the strand I3 by each cycle of alternating current strand I3, and accordingly,

thereof. Accordingly,

3| and 33. The longitudinal forces thus exerted tend to sustain transverse vibration of the strand I3 at its natural period of vibration.

Coils 3|, 33 may be made to exert sufficiently strong forces on the strand I3 to provide full compensation for energy loss accompanying transverse vibratory movement of this strand, vas due both to gas damping within the envelope II and to the molecular friction within strand I3 l0 caused by the alternate elongation and contraction thereof. Under such a condition, the strand I3 would be retained in transverse vibration even if potentiometer 31 were adjusted for zero output voltage, eliminating the current through the eliminating the transverse drive component therefor. However, in most practical applications, it is desirable that some degree of control be exercised upon the strand to regulate the direction of vibration the longitudinal drive curcondition of insufficiency for fully sustaining the vibration of the strand I3, and the potentiometer 31 is adjusted in such a way that the deficiency of the longitudinal drive rent is adjusted to a 25 is made up by the transverse driving forces exerted by the electric motor reaction of the alternating current through strand I3 with the ambient magnetic field component.

In order to facilitate the ideal proportioning of the settings of potentiometers 31 and 41 for a desired degree of transverse control over the plane of vibration of strand I3, and to facilitate the adjustment of these potentiometers to a condition in which the total driving forces acting 35 upon the strand I3 are just sufficient to maintain of the the vibration thereof at a desired constant amplitude, amplifier 21 may include an amplitude limiting stage or an automatic gain control circuit arr-anged to suppress changes of output voltage amplifier. Such circuits are not absolutely essential, however, as amplifiers are inherently limited by the characteristics of the vacuum tubes and supply circuits ordinarily provided.

For convenience in utilization of the stable reference propensities afforded by the vibration oi strand I3, -a second capacitor pick-off plate 5I may be supported in proximity to the strand I3, anc' may be arranged to supply an alternating signa upon angular departure about the axis of stran:

I3 from a predetermined angular relation between 51 to the input circuit of 00 former 29, and

the plane of vibration of strand I3 and the en velope II. Capacitor pick-ofi element 5I may b energized by a voltage source 55 through a re sistor 53, and may be coupled through a capacite an amplifier 59 arrange to supply an amplified alternating voltage to th input circuit of a phase sensitive amplifier 5 Unit GI is supplied with a phase reference voltar by an auxiliary secondary winding 53 of tran: this amplifier 5I supplies a dire output voltagev of magnitude and polarity varyir according to the amplitude of the voltage supplia from amplifier 59 and the phase of this voltal relative to the phase of the voltage from seconda winding 63.

The output voltage from phase sensitive amp iler 6I may be supplied to control terminals such as field winding terminals of a reversil motor $1, which may have a principal pair power input terminals such as armature t1 through coils 7 strand Il, and accordingly, the strand 'Il itself, tive forces directly within a magnetostrictively in such a way as to suppress the alternating susceptible strand I3, such transverse disturbvoltage developed in capacitor pick-off elementv ance is minimized or substantially eliminated. Il.

envelope Il may be pivotally suspended in a craft larly, for providing a stable reference about a such as anfaircrai't for rotation about a vertical vertical axis in predetermined relation to the di axis. In such a use of the invention, the motor rection of the horizontal component of the Il is fixed to the aircraft and employed for rei0 earth's magnetic field, it will be readily apparent taining gear element .1I and the elements asthat the longitudinal drive features of the' pressociated therewith fixed in space about the verent invention are readily usable in` other artical axis, by reference to the plane oi vibration rangements. as for example, where the ambient of the strand I3. This system then serves as a magnetic field for sustaining vibration is prostabilized magnetic compass, if the earthsma'p 15 vided by a local vmagnetic system, whether the netic field is employed as the ambient neld for strand is normally aligned vertically or hortreaction with the current through' the strand I3. zontally, or in a direction oi' intermediate in- Where the earth's magnetic neld is thus permitclination. ted to act directly on the strand. the strand I3 While the features of the present invention vibrates in the vertical east-west plane, i. e., relieve" to some extent the dependency upon obn in the vertical plane perpendicular to the horitaining very high of the vibratory system zontal component of the earth's magnetic neld. for enhancement of stability thereof, and make Accordingly, element 1l may be engraved with possible the provision or a moderately long-time compass rose directional designations, the east stability where the or the mechanical citiwest designations being aligned parallel with the ciency or the vibratory system is relatively low, eifective surface of capacitor element il. it may none-the-less be desirable to provide rela With this arrangement, so long as element 'Il tively high "Q in order that extremely high remains properly oriented in space relative to stability be achieved. For this reason, it is confore. motor l1 is inactive. Upon rotation of the ated, so that a desired set oi performance charcraft about'the vertical axis, however, as when acteristics may be obtained according to the ex a turn of the craft is commenced, there is a tend tent to which this structure is evacuated.

ency to turn gear element ll from its prede- Since many changes could be made in the termined orientation relative to the earth's field, 40. above construction and many apparently widely and as it commences to revolve with the craft, diifercnt embodiments o1' this invention could an alternating voltage is supplied to the input be made without departing from the scope therem circuit of amplifier Il as the face oi' pick-off of, it is intended that all matter contained in the element Il becomes non-parallel with theplane above description or shown in the accompanying of vibration of the strand I3. Under these condrawings shall be interpreted as illustrative and ditions, the phase sensitive amplifier Il supplies not in a limiting sense.

to motor 61 a /voltage oi.' the polarity required to What is claimed is:

urge element 1l in the direction to restore the i. Stable reference apparatus comprising a and the plane oi vibration of the strand I3. Units stretched between two points in said supporting` hence, to hold the directionally calibrated eleu tional pick-off means for producing an output ment 15 in correct orientation in azimuth relasignal varying according to the direction of the tive to the earth's magnetic neld. transverse plane of vibration oi said strand, and

In Fig. 1, the magnetostrictive driving coils means responsive to said signal for controlling the Il. 33 are illustrated as supported within endirection of said pick-oil' means to maintain a velope I| for concentration of their magnetic go predetermined directional relation -between said coil I2. SUI'IOUndiIls the envelope Il. While Dart 65 tibie material stretched between two points in or all of the magnetostrictive drive could be exsaid supporting member, means for producing an ercised upon the ferrules Il and l1, ii' desired, alternating magnetic field along said strand for I l, in view ofthe dimculty of providing such pre- 7o pick-oil means coupled to the strand for produc- 3. In combination, a supporting member, a strand of elastic and magnetostrictively 'susceptible material stretched between two points in said supporting member, electromagnetic coil means aligned with said strand for producing' a magnetic field extending therealong, and means responsive to vlbratory movement of said strand for supplying to said coil means energizing alternating current of frequency and phase determined by the movement of said strand for sustaining vibration of said strand.

4. In combination, a supporting member, a strand of elastic material stretched between two points in said supporting member, alternating current means for varying the tension in said strand at a frequency double the frequency of the current, and means responsive to transverse vibration of said strand for supplying to said lastnamed means alternating current of the frequency of transverse vibration of said strand. whereby the tension of said strand is varied at the frequency of the elongation and contraction thereof. Y

5. In combination, a supporting member, a strand of elastic material stretched between two points in said supporting member, alternating current responsive magnetostrictlve means for exerting longitudinal forces on said strand at a;

frequency double the frequency of an applied current to cause transverse vibration of said strand, and means responsive to transverse' vibration of said strand for supplying to said lastnamed means alternating current of the frequency of transverse vibration of said strand, whereby the tension of said strand is varied at the frequency of the elongation and contraction thereof.

6. In combination, a supporting member, a strand of elastic material stretched between two points in said supporting member, means for exerting both relatively great alternating longitudinal forces and relatively slight alternating transverse forces on said strand, and means responsive to transverse vibration of said strand for controlling the frequency of said force exert ing means whereby said strand is transversely vibrated for endowment with orlentational stability and the transverse directional influence is rendered relatively slight accordingly as the vi'- bration sustaining power is principally supplied by the longitudinal forces.

7. In combination, a supporting member, a strand of elastic and magnetostrictive material stretched between two points in said supporting member, and means for magnetostrictively exerting alternating longitudinal forces on said strand and for electromagnetically exerting alternating transverse forces on said strand whereby said strand is transversely vibrated for endowment with orientational stability in a plane determined by the time integral of the directions of transverse drive over a period rendered relatively long accordingly as the vibration sustaining power for said strand is principally supplied by the longitudinal magnetostrictive force exerted thereon.

8. In combination. a supporting member, al

strand of elastic material stretched between two points in said supporting member, and means for passing alternating current through said strand to provide transverse force reaction with an ambient magnetic field and for exerting alternating longitudinal forces on said strand, whereby said strand is maintained in vibration transverse said ambient magnetic field and endowed with orientational stability transverse said field, said means being so constructed and arranged that the vibration sustaining power supplied through said longitudinal forces exceeds the power supplied through said transverse forces, whereby the transverse directional influence of said field is rendered relatively slight. l

9i In combination, a supporting member, a strand of elastic and magnetostrictively suscepl0 tible material stretched between two points in said supporting member, and means for passing alternating current through said strand for producing transverse force reactions with an ambient magneticl field and for providing an alternating magnetic field component along said strand for exerting alternating "longitudinal forces thereon, whereby said strand is vibrated transversely of said ambient magnetic field and thereby endowed with orientations! stability, and the burden of sustaining the vibration of said strand is partially borne by the manetostrictive drive in such a way as to limit the directional coercion on the direction of vibration of said strand due to the force reactions in said ambient magnetic ileld.

l0. In combination, a supporting member, a strand of elastic material stretched between two points in said supporting member, and means for exerting both alternating longitudinal forces and alternating transverse forces on said strand, said alternating longitudinal forces including a component at twice the frequency of the alternating transverse forces, whereby said strand is transversely vibrated for'endowment of orientational 35 stability and such a part of the burden of sustaining the vibration of said strand is borne by the longitudinal drive forces as to limit the transverse directional coercion on said strand for longtime stability thereof. 40 1l. In combination. a supporting member, a strand of elastic material stretched between two points in said supporting member, means respon sive to vibration of said strand for producing an alternating current at the frequency of vibration of said strand, and means utilizing said alternating current for exerting alternating transverse forces on said strand at the frequency of said current and for exerting alternating longitudinal forces on said strand at a frequency twice the frequency of said current whereby said strand is transversely vibrated at its natural frequency for endowment lwith orientational stability and a predetermined part of the burden of sustaining the vibration of said strand is made noncoercive as to the direction of transverse vibration thereof for enhancement of the long-time stability of the direction of vibration of the strand.

12. Stable reference apparatus comprising a tubular envelope, a strand of elastic material 50 stretched between two points axially displaced along said envelope, said envelope being substantially evacuated to ize damping of vibration of said strand. and electromagnetic coil means fixed to said envelope in substantially coes axial relation with said strand and adapted to be energized by alternating current for periodi-l cally varying the tension in said strand to provide transverse plane of vibration of said strand 3 and to endow it with vibration directional stability.

13. In combination. a tubular envelope, a strand of elastic and magnetostrictively susceptible material stretched between two points axial-v ly displaced in said envelope. said envelope being substantially -e to minimize gaseous damping of vibration of said strand, and means including an electromagnetic coil fixed to said envelope in a position of substantially coaxial with said strand for producing an alsaid axis to restore said predetermined alignment.

18. Stable reference apparatus claim 17, wherein said predetermined axis is veraction with the earths magnetic eld.

coupled to said signal varying according to bration. Y

20. A stable reference element driven longitudinally -by magnetostriction and synchronously driven transversely, and means including a vibration pick-off coupled to said element and an aman output its direction of vitransverse drive of said element.

21. Stable reference apparatus supporting member, a, strand of THOMAS M FERRILL. Jig. REFERENCES onen The following references are of record in the ie of this patent:

UNITED STATES PATENTS Number Name Datey 1,616,416 Fessenden Feb. 1, 1927 2,120,985 Melhose June 21, 1938 2,223,537 Sykes Dec. 3, 1940 

